I. Field of the Invention
This invention relates to detection of ectopic beats in the heart by analyzing Q*R time intervals on cardiac electrograms.
II. Description of the Related Art
Time-domain analysis has been widely used to detect premature ventricular contraction (PVC) caused by an ectopic beat. This analysis is based on the relationship between sensed atrial depolarization P and/or ventricular depolarization R. For example, a sensed ventricular beat R without a preceding sensed atrial beat P is considered a PVC. Other examples of PVCs are, a ventricular beat R that is sensed very shortly after sensing atrial activity P or a sensed ventricular beat R with a sudden shortening ventricular beat interval.
Although time-domain analysis with the timing of ventricular beats R and atrial beats P is simple and easy to use, it has limited applications. For example, it can only detect ectopic beats that occur significantly earlier than beats in normal cycles. Yet a ventricular ectopic beat can occur at any time, regardless of the preceding atrial or ventricular events. An ectopic beat can occur after a sensed atrial beat without a very-short PR or RR interval and is thus mistakenly interpreted as a normal beat. Similarly, a post ventricular atrial refractory period (PVARP) of an implanted pacemaker that is triggered by an ectopic beat could mask the pacemaker""s detection of the next P-wave, making the system falsely double-count PVCs.
Morphology analysis has also been employed instead of time-domain analysis because ventricular ectopic beats tend to have different shapes in electric response signal than normal ventricular beats or super-ventricular ectopic beats. Yet, such analysis is much more complicated than the time domain analysis.
Furthermore, the prior art methods of detecting ectopic beats using either external ECG equipment or implanted dual chamber pacemakers or pacemaker/defibrillators cannot accurately pinpoint the source of the ectopic beats. Such information may be useful in treating patients with arrhythmia.
In implementing the present invention, a cardiac rhythm management device is programmed to measure the time interval between the earliest activation of the ventricular polarization, referred to herein as Q*, and the peak of the following ventricular depolarization signal, R. The measured interval is referred to as T and is equal to the time between the Q* point on the QRS complex and R or T=Q*R. The mean value of T and standard deviation are calculated dynamically on a beat-to-beat basis from normal heartbeats for the patient being monitored. It has been empirically determined that any T values of a given beat greater than about 4 standard deviations of the mean T value is considered to be associated with an ectopic beat.
The algorithm for measuring for ectopic beats described herein have several advantages over known prior art methods. Prior art methods have used the PR interval or the RR interval to determine if an ectopic beat has occurred. But, as mentioned above, ectopic beats occur independently of the PR or RR intervals, making these prior art methods unreliable indicators of ectopic beats.
Another advantage of using the T=Q*R interval method of the present invention is that if more than one electrode is used, the location or origin of ectopic excitation can be estimated.
The Q*R method described herein is based somewhat on morphology rather than purely on timing since the ectopic beat can originate from anywhere at any time. Therefore the Q*R method combines the advantages of timing and morphology methods to improve the detection of ectopic beats.
More accurate diagnosis of arrhythmias and better performance of pacemakers incorporating the ectopic beat detection algorithm of the present invention can result from a utilization of this invention.
It is a principal object of the invention to providing an algorithm for a microprocessor-based cardiac rhythm management device that accurately detects the occurrence of ectopic beats in the heart.
It is a further object of the invention to provide a simpler method for detecting ectopic beats in the heart than used in prior art systems.
Another object of the invention is to provide an ectopic beat detector utilizing only one ventricle sensor and no atrial sensor.
It is an object of the invention to provide an ectopic beat sensing algorithm that is capable of detecting where an ectopic beat originates within the heart.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings